1. Field of the Invention
The present invention relates to a mobile communication terminal, particularly, to a mobile communication terminal equipped with a loop antenna housed in the casing of the mobile communication terminal.
2. Description of the Related Art
A loop antenna in which the directivity characteristics of radiated electric wave is controlled is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 2001-237637. In the loop antenna disclosed in Japanese Patent Disclosure No. 2001-237637 referred to above, a waveguide plate having a surface parallel to the plane of the loop antenna is arranged at a position a prescribed distance apart from the plane of the loop antenna in the vertical direction. The loop antenna exhibits the radiation characteristics of the electric wave having a directivity in a direction perpendicular to the plane of the loop antenna. Particularly, the loop antenna exhibits the greatest radiation characteristics toward the waveguide plate. In this fashion, the loop antenna is combined with the waveguide plate so as to utilize the loop antenna as a primary radiator of a parabolic antenna.
In the case of using a loop antenna in a portable telephone, the line length of the loop antenna that is determined by the wavelength is rendered considerably large. Since the loop antenna is housed in the portable telephone, the line length of the loop antenna is secured by arranging the front surface of the portable telephone on which is positioned the receiver in parallel to the plane of the loop antenna.
Where the loop antenna disclosed in Japanese Patent Disclosure No. 2001-237637 referred to above is mounted to the portable telephone of the construction described above, a radiation energy is generated in a direction perpendicular to the plane of the loop antenna, i.e., the radiation energy is generated toward the user of the portable telephone. As a result, a mismatch loss and a dielectric loss is generated on the basis of the human body forming a dielectric element so as to give rise to the problem that the radiation efficiency of the antenna is lowered.